During operation of a gas turbine engine using a multi-stage axial compressor, a turbine rotor is turned at high speeds by a turbine so that air is continuously induced into the compressor. The air is accelerated by rotating blades and swept rearwards onto adjacent rows of variable stator vanes. Each rotor blade/variable stator vane stage increases the pressure of the air.
In addition to translating the kinetic energy of the air into pressure, the variable stator vanes also serve to correct the deflection given to the air by the rotor blades and to present the air at the correct angle to the next stage of rotor blades. Pivoting the variable stator vanes permits the flow capacity of the compressor or turbine to be changed, thereby ensuring that the flow capacity is always at an optimum value for the particular operating conditions of the gas turbine engine.
The operating efficiency of the gas turbine may be improved by operating the compressor at a relatively high pressure ratio. However, if the pressure ratio is allowed to exceed a certain critical value during turbine operation, an undesirable condition known as compressor stall may occur. Compressor stall may reduce the compressor pressure ratio and reduce the airflow delivered to a combustor, thereby adversely affecting the efficiency of the gas turbine. Rotating stall in an axial-type compressor typically occurs at a desired peak performance operating point of the compressor. Following rotating stall, the compressor may transition into a surge condition or a deep stall condition that may result in a loss of efficiency and, if allowed to be prolonged, may lead to catastrophic failure of the gas turbine. Accordingly, there is a need to detect and prevent compressor stall.